Scott - each succeeding higher number superceded the lower (minor design changes). The higher number would be the most desirable, but all are excellent. The "Z" prefix is short for "Zip-fit", Carter's terminalogy for a replacement unit.

There were also some much newer YF carbs made for Chevrolet 6 cylinders in the mid-1960's, but these are not included in this list. The carburetors listed are for Chevrolet 181, 206, 216 and 235 CID engines beginning in 1932.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop